Have you tried overnight treatments lately with something else, another oil or conditioner? If you haven't, you might want to try that soon and see if the smell comes back. Bacteria and fungus thrive in dark, moist and warm places, and overnight treatments could add up to the perfect storm, so to speak ... so that you may have a mild infections that doesn't make itself obvious until you do treatments.

If not, I guess you'll just stay away from coconut treatments and hope it's not an underlying infection.
3b/c?

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